refactor(pi-compaction): 改为压力触发的观察遮蔽与空闲阈值整段摘要

原实现对所有工具结果（含 read）在下一次请求即替换为约 4K 的首尾存根，
不看上下文压力，导致模型看不到大文件中段；后台逐条语义摘要又反复改写
历史、打碎 prompt 缓存。参照 Anthropic 上下文编辑、Manus 与 JetBrains
观察遮蔽研究重构为：
- L2：上下文达到阈值时在 turn_end 批量提交 Pi 原生 context_edit，把最近
  keepRecentTurns 轮之外的旧 toolResult 换成确定性占位符；trigger/target
  回差与 minClearTokens 保证少触发、一次清够；原始条目保留，可经
  context_tree_query 取回
- L3：空闲 agent_settled 且超过绝对阈值时调用一次 ctx.compact
- 阈值按绝对 token 计并受窗口比例约束，默认针对 1M 窗口（DeepSeek V4.1
  Flash）：遮蔽 200K→100K、整段摘要 400K
- 删除逐条存根、语义 worker、soft/hard/target 比例与自行取消 Pi 压缩的门控；
  Pi 原生阈值压缩保留为最终安全网

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

pi-compaction/test/segment-index.test.ts

@@ -1,7 +1,6 @@
 import test from "node:test";
 import assert from "node:assert/strict";
-import { DEFAULT_CONFIG } from "../src/config.ts";
-import { SegmentIndex, deterministicSummary } from "../src/segment-index.ts";
+import { SegmentIndex } from "../src/segment-index.ts";
 
 const assistant = {
   role: "assistant",
@@ -17,66 +16,96 @@ const result = {
   timestamp: 11,
 };
 
-test("deterministic summary is bounded and preserves head/tail evidence", () => {
-  const summary = deterministicSummary({
-    toolName: "bash",
-    args: { command: "npm test" },
-    rawText: result.content[0]!.text,
-    isError: true,
-    maxStubTokens: 256,
+// Regression: a ~14.5K-char read result projected under a 1M window must reach
+// the model byte-for-byte unchanged — masking only happens via context_edit
+// drafts under real pressure, never on the hot projection path.
+test("projection is byte-for-byte identity for a 300-line read result under a 1M window", () => {
+  const readBody = Array.from({ length: 300 }, (_unused, index) => `line ${index + 1}: ${"y".repeat(38)}`).join("\n");
+  const readResult = {
+    role: "toolResult",
+    toolCallId: "call-read",
+    toolName: "read",
+    content: [{ type: "text", text: readBody }],
+    timestamp: 12,
+  };
+  assert.ok(readBody.length > 14_000 && readBody.length < 15_000, `fixture ${readBody.length} chars`);
+
+  const index = new SegmentIndex("session-1");
+  index.hydrate();
+  const snapshot = index.project([assistant, readResult], {
+    environmentHash: "env",
+    environmentTokens: 100,
+    contextWindow: 1_000_000,
+    maskedResults: 0,
+    reclaimedTokens: 0,
   });
-  assert.match(summary, /tool=bash status=error/);
-  assert.match(summary, /failure/);
-  assert.match(summary, /stack tail/);
-  assert.ok(summary.length <= 1_100);
+
+  assert.strictEqual(snapshot.messages[1], readResult);
+  assert.strictEqual(snapshot.messages[1]!.content[0].text, readBody);
+  assert.ok(snapshot.messages[1]!.content[0].text.includes("line 150:"));
+  assert.equal(snapshot.reclaimedTokens, 0);
+  assert.equal(snapshot.maskedResults, 0);
 });
 
-test("projection incrementally replaces tool results and caches identical input", () => {
-  const index = new SegmentIndex("session-1");
-  index.hydrate([], DEFAULT_CONFIG);
-  const records = index.captureTurn(assistant, [result], DEFAULT_CONFIG);
-  assert.equal(records.length, 1);
-
+test("projection caches identical input and handles append-only deltas", () => {
+  const index = new SegmentIndex("session-2");
+  index.hydrate();
   const messages = [assistant, result];
-  const first = index.project(messages, {
-    environmentHash: "env",
-    environmentTokens: 100,
-    contextWindow: 300_000,
-  });
-  const second = index.project(messages, {
-    environmentHash: "env",
-    environmentTokens: 100,
-    contextWindow: 300_000,
-  });
-
+  const params = { environmentHash: "env", environmentTokens: 100, contextWindow: 300_000, maskedResults: 0, reclaimedTokens: 0 };
+  const first = index.project(messages, params);
+  const second = index.project(messages, params);
   assert.strictEqual(first, second);
-  assert.ok(first.effectiveTokens < first.rawTokens);
-  assert.match(first.messages[1]!.content[0].text, /context_tree_query/);
+  assert.ok(first.rawTokens > 0);
 
-  const record = records[0]!;
-  assert.ok(index.applySemantic(record.sourceKey, record.sourceHash, "- npm test failed\n- stack tail"));
-  const semantic = index.project(messages, {
+  const appended = index.project([...messages, { role: "user", content: "next", timestamp: 13 }], params);
+  assert.notStrictEqual(appended, first);
+  assert.equal(appended.messages.length, 3);
+  assert.strictEqual(appended.messages[1], result);
+});
+
+test("changed masking stats publish a new snapshot without mutating the old one", () => {
+  const index = new SegmentIndex("session-stats");
+  index.hydrate();
+  const params = {
     environmentHash: "env",
     environmentTokens: 100,
     contextWindow: 300_000,
-  });
-  assert.notStrictEqual(semantic, first);
-  assert.match(semantic.messages[1]!.content[0].text, /npm test failed/);
+    maskedResults: 0,
+    reclaimedTokens: 0,
+  };
+  const first = index.project([assistant, result], params);
+  const same = index.project([assistant, result], params);
+  assert.strictEqual(same, first);
+
+  const updated = index.project([assistant, result], { ...params, maskedResults: 1, reclaimedTokens: 500 });
+  assert.notStrictEqual(updated, first);
+  assert.equal(updated.maskedResults, 1);
+  assert.equal(updated.reclaimedTokens, 500);
+  assert.equal(updated.rawTokens, updated.effectiveTokens + 500);
+  // The previously published object stays immutable.
+  assert.equal(first.maskedResults, 0);
+  assert.equal(first.reclaimedTokens, 0);
+  // Unchanged stats keep returning the same cached object.
+  assert.strictEqual(index.project([assistant, result], { ...params, maskedResults: 1, reclaimedTokens: 500 }), updated);
 });
 
 test("usage-backed baseline is adjusted only by projected delta", () => {
-  const index = new SegmentIndex("session-2");
-  index.hydrate([], DEFAULT_CONFIG);
+  const index = new SegmentIndex("session-3");
+  index.hydrate();
   const initial = index.project([assistant], {
     environmentHash: "env",
     environmentTokens: 50,
     contextWindow: 100_000,
+    maskedResults: 0,
+    reclaimedTokens: 0,
   });
   index.recordUsage(1_000, initial.messageEstimate, "env");
   const next = index.project([assistant, { role: "user", content: "next", timestamp: 12 }], {
     environmentHash: "env",
     environmentTokens: 50,
     contextWindow: 100_000,
+    maskedResults: 0,
+    reclaimedTokens: 0,
   });
   assert.equal(next.confidence, "usage-backed");
   assert.ok(next.effectiveTokens >= 1_000);